Storage devices for sheet materials such as paper or plastic film exist in a variety of shapes and constructions. One representative storage device is the ring binder, containing a front cover, back cover and spine, which encloses a two or three ring binding element which can be opened to introduce punched paper or similar sheet-like material and then reclosed. These binders are relatively expensive to manufacture because of both the cost of the binder mechanism and the labor to secure this mechanism onto the spine of the binder cover. In addition, the metal binder rings, particularly in larger dimensions, tend to become misaligned with use. As a result, over time the stored sheets do not turn freely over the rings, and can occasionally become ripped from the misaligned metal.
Another known binder device for punched sheets uses spaced flexible metal straps which are secured to a binder cover. These metal straps are in turn fed through holes punched in paper or similar sheet-like material and then secured in place by feeding the straps through holes in a separate upper plate and attaching the straps to the plate. This binder device does not permit the punched sheets to freely rotate in the metal straps. Rather, the sheets are maintained in a single orientation. With repeated opening and closing of the binder mechanism the metal straps become bent and do not attach as efficiently to the plate.
Yet another binding device incorporates a releasable tensioned plate secured to a binder cover which permits insertion of the sheets to be stored followed by tightening of the tensioning device. This binding device does not require prior hole punching of the sheets. Nonetheless, the device is susceptible to loosening, resulting in loss of sheets from the binding device. If the quantity of sheets becomes too large, it is possible for sheets near the center to fall out of the device even with the stack under tension. Also, the sheets are only maintainable in a single orientation; they cannot rotate relative to the tensioned plate.
Each of the above binder device designs permits the storage of a variable number of pages. Nonetheless, these designs incorporate binding mechanisms which require relatively complex manufacturing steps and the expenditure of labor in installing these mechanisms into a binder, as well as having deficiencies in effectively storing sheet materials.
There remains a need for a binder device which will effectively store a variable number of pages and will retain all stored pages, yet at the same time provide easy access to individual pages. It is also preferred that this type of binding device be produced inexpensively and be able to be used and reused with little risk of damage to the device or the stored sheets.